1. Field of the Invention
The present invention relates to electrically connecting terminal structures for a circuit board and a manufacturing method of the structures, and more particularly, to a method for manufacturing an electrically connecting terminal structure of a circuit board by electroplating.
2. Description of the Prior Art
Flip chip package technology was introduced into the industry by IBM in the early 1960s. Unlike wire bonding technology, flip chip package technology involves implementing electrical connection between a semiconductor chip and a circuit board by solder bumps instead of gold wires. Flip chip package technology spares the use of long gold wires and thereby enables reduction of impedance. In view of this, the technique of applying high-temperature solder to a ceramic substrate, or control collapse chip connection (i.e., “C4”), has been in use for years. Recent years saw an increasing demand for high-density, high-speed, low-cost semiconductor components and a trend toward miniaturization of electronic products, and thus there is explosive growth in installing flip-chip components in low-cost circuit boards and disposing resin underfill beneath a chip to decrease the thermal stress resulting from a thermal expansion difference between a chip and an organic circuit board.
With the existing flip chip technology, an integrated circuit (IC) chip is equipped with electrode pads that match electrically connecting pad of an organic circuit board, and solder bumps or any other conductive surface-mounted materials can be disposed between the chip and the circuit board as appropriate, and thus the solder bumps or the other conductive surface-mounted materials provide electrical input/output (I/O) and mechanic connection between the chip and the circuit board.
As shown in FIG. 1, flip chip technology involves forming a plurality of metal bumps 11 on electrode pads 12 of a chip 13, forming a plurality of presoldered bumps 14 (made of a solder material) on electrically connecting pads 15 of a circuit board 16, reflowing the presoldered bumps 14 at a reflow temperature such that the presoldered bumps 14 and the corresponding metal bumps 11 together form solder joints 17, and disposing an underfill material 18 beneath the chip 13 so as to ensure the integrity and reliability of the electrical connection between the chip 13 and the circuit board 16.
To enhance electrical performance of an electronic device, it is necessary to install passive components, such as resistors, capacitors, and inductors, in the electronic device. In general, the passive components are mounted on a circuit board by surface mount technology (SMT), and thus presoldered bumps and surface-mounted soldered components are found on the circuit board concurrently, with a difference between both in terms of the height and size of a presolder material formed.
Afterward, during an encapsulation process performed on the circuit board, semiconductor chip, and passive component, it is necessary to implant a plurality of solder balls beneath the circuit board so as to electrically connect the circuit board with any external electronic device. To mount the solder balls on circuit board efficiently, it is necessary to form a presolder material on the electrically connecting pads of the circuit board so as to allow the solder balls to be mounted on the electrically connecting pads of the circuit board by means of the presolder material.
A presolder material is usually formed on electrically connecting pads of a circuit board by electroplating. FIGS. 2A-2F are cross-sectional views showing a conventional method for electroplating a solder material onto electrically connecting pads of a circuit board.
As shown in FIG. 2A, the conventional method comprises: providing a circuit board 2 having a surface formed with a plurality of first electrically connecting pads 20 and second electrically connecting pads 22 of different sizes, wherein the surface of the circuit board 2 is formed with a circuit structure (not shown), the first electrically connecting pads 20 are, for example, presoldered bump pads intended to be connected to a flip chip, and the second electrically connecting pads 22 are, for example, surface-mounted (SMT) pads for connection with passive components or ball pads for ball implantation. The first and second electrically connecting pads 20 and 22 are formed on either the same surface or different surfaces of the circuit board 2.
As shown in FIG. 2B, the conventional method further comprises forming an insulated protecting layer 23 on the circuit board 2, forming in the insulated protecting layer 23 a plurality of openings 230 for exposing the first and second electrically connecting pads 20 and 22 on the circuit board 2.
As shown in FIG. 2C, the conventional method further comprises forming a conductive layer 24 on the insulated protecting layer 23 and the openings 230 thereof, forming a resist 25 on the conductive layer 24, forming in the resist 25 a plurality of openings 250 corresponding in position to the openings 230 of the insulated protecting layer 23 and exposing the conductive layer 24 on the first and second electrically connecting pads 20 and 22.
As shown in FIG. 2D, the conventional method further comprises electroplating metal bumps 26 and a presolder material 27 onto the first electrically connecting pads 20 in sequence, electroplating metal bumps 28 and a presolder material 29 onto the second electrically connecting pads 22 in sequence, using the conductive layer 24 as an electrical conduction path.
As shown in FIG. 2E, the conventional method further comprises removing the resist 25 and the conductive layer 24 thereunder.
As shown in FIG. 2F, the conventional method further comprises performing a reflow process on the presolder materials 27 and 29 at a melting temperature thereof such that solder structures 27′ and 29′ of different heights and sizes are formed on the first and second electrically connecting pads 20 and 22, wherein the solder structure 27′ of a relatively great height functions as a presoldered bump for mounting a semiconductor chip, and the solder structure 29′ of a relatively small height is to be mounted with a passive component, such as a surface-mounted device, or is to be implanted with solder balls.
Although the aforesaid conventional process enables the metal bumps 26 and 28 and the solder materials 27 and 29 to be formed on the first and second electrically connecting pads 20 and 22 with different sizes on the circuit board 2, the relatively large-sized second electrically connecting pads 22 are formed with the metal bumps 28 of a considerable height; as a result, whatever presolder materials subsequently formed on the metal bumps 28 are too high, thus allowing an overflow or shift to occur to the solder materials on the second electrically connecting pads 22 during a subsequent reflow process, and compromising the quality and reliability of the solder materials. In consequence, the reliability of a subsequent process of mounting passive components on the electrically connecting pads of the circuit board or a subsequent ball implantation process is affected to a great extent.
In addition to poor quality and reliability of the solder materials of a circuit board, the prior art does have another drawback, that is, the fine pitch requirements for the electrically connecting pads of high-level electronic products cannot be met.
Accordingly, an issue calling for immediate solution involves developing a method for manufacturing an electrically connecting terminal structure for a circuit board so as to solve the drawbacks of the prior art, that is, poor quality of the solder materials fabricated by a reflow process and failure to meet the fine pitch requirements.